This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 09 373.6, filed on Feb. 29, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to an air conditioning system especially for a passenger aircraft that includes at least one rotational shaft with a rotary compressor and a rotary turbine mounted thereon, to provide at least one compression stage and at least one expansion stage of an air cycle cooling process. The air conditioning system especially provides a redundant or auxiliary ventilation.
In all known aircraft having an integrated air conditioning system, the required cooling energy is recovered from highly compressed engine bleed air, through an air cycle including a thermodynamic air compression and expansion process with an intermediate cooling of the compressed air. Various condensation processes are provided in the circuit for drying, i.e. removing moisture from, the air. Other cooling processes are also known, in which the compression and expansion processes are at least partially replaced by hybrid cooling processes, for example in order to compensate for insufficient pressure energy from the engine bleed air. These compression and expansion processes can be circuit-connected in various manners, whereby these processes are typically carried out by turbo-machines including compressors and turbines mounted on rotating shafts.
In this context, the number of rotating shafts and the number of turbo-machines can be varied, which leads to different characteristic properties or behaviors of the overall respective system. In any event, it is of course physically required to achieve an energy balance, i.e. a balanced energy equation, for all of the energetically relevant devices (turbo-machines, compressors, turbines, blowers, etc.) mounted on each respective shaft. In other words, for each rotating shaft, the energy input necessarily equals the energy output. This must be taken into account when arranging different rotary devices on a respective shaft.
Moreover, air cycle cooling processes are known that operate with one stage compression and one stage expansion, one stage compression and two stage expansion, as well as two stage compression and two stage expansion. Examples of such cooling processes and arrangements are disclosed in U.S. Pat. Nos. 5,086,622 and 5,887,445. These known processes and apparatus respectively work with different combinations and arrangements of compressors and turbines mounted on various shafts, whereby the compressors and turbines are incorporated into the main air cycle.
In any event, an energy balance must always be maintained per each shaft, whereby the energy output of the total system is achieved by the respective particular circuit connection of the shafts and the turbo-machines, and in view of the energy input of the hot compressed engine bleed air. In this context, furthermore, the air conveying and throttling apparatuses, the intercooling unit, and the condenser group that are allocated to and connected to the turbo-machines must be tuned or adapted with regard to their size and efficiency, to properly match the total energy to be output from the system.
The energy that is transferred and transformed through such a cooling unit or air conditioning pack is unavoidably associated with power losses, which are given off as thermal heat energy and/or particularly thermal radiation, into the installation environment immediately surrounding the cooling unit. As a result, if such a cooling unit is integrated into an enclosed space in an aircraft, then this power dissipation in the form of heat will be given off into the surrounding space, which will directly increase the temperature of the air in this space as well as the surrounding aircraft structure.
The above mentioned heating of the installation space in which a cooling unit is installed in an aircraft is undesirable, because the installation space may overheat and require the cooling unit to be shut down, unless the heat can be removed from the installation space. Therefore, the excessive heating of the installation space has been counteracted in some aircraft by installing a forced ventilation system driven by an external energy source to achieve a positive ventilation of the installation space. This forced positive ventilation system is operated so as to achieve a comfortable or acceptable temperature range of the pertinent space. A separate turbo-compressor machine may be used as the external energy source for providing the positive ventilation air flow. Namely, a turbine connected to a rotatable shaft is driven by energy-rich engine bleed air so as to drive the shaft with a shaft power that is provided for driving the compressor mounted on this shaft. The compressor in turn takes in a quantity of external air, compresses it to the required pressure level and provides the resulting compressed air through a connected air distribution network to the surrounding installation spaces in which the air conditioning units are installed, so as to achieve a positive forced ventilation of these spaces. This achieves a suitable cooling of these installation spaces, as long as the separate turbo-compressor continues operating properly. However, if this separate turbo-compressor fails for any reason, then the positive forced ventilation and cooling of the installation spaces of the air conditioning units will not be provided, whereupon these spaces and the associated air conditioning units will overheat and must necessarily be shut down.
In view of the above, it is an object of the invention to provide an air conditioning system especially for a commercial passenger transport aircraft, which reliably provides a redundant supply of ventilation air through an air distribution network to all areas or spaces within the aircraft that are connected to this air distribution network. It is a further object of the invention to provide a reliable positive forced ventilation and cooling of the installation space in which an air conditioning unit is installed, whereby this ventilation is necessarily reliably maintained whenever the air conditioning unit is operating.
The above objects have been achieved according to the invention in an air conditioning system for an aircraft, including a first rotatable shaft with a first compressor and a first turbine connected thereto so as to rotate together with the shaft. Further according to the invention, an additional auxiliary compressor is connected to the first shaft, and a ventilation or auxiliary air line is connected to an outlet of the auxiliary compressor, such that compressed air provided by the auxiliary compressor is transported through the ventilation air line. An air inlet of the auxiliary compressor is connected to the outside environment surrounding the aircraft, or to the internal environment within the aircraft surrounding the auxiliary compressor, or even to some other source of air.
Throughout this specification, an air xe2x80x9clinexe2x80x9d generally refers to any duct, hose, pipe, channel or the like, through which air can be conveyed and directed. The auxiliary air line will also be referred to as a ventilation air duct, for example, in the following embodiments. The general term xe2x80x9cair-moving devicexe2x80x9d refers to a compressor, a turbine, a blower, a fan, an air pump or the like, which moves or is moved by a flow of air and which converts mechanical rotation power to air-flow power or vice versa. Any compressor referred to herein, including the auxiliary compressor, can be embodied as a radial flow compressor, an axial flow compressor, or a diagonal flow compressor. A compressor, a turbine, or a fan is considered xe2x80x9cconnectedxe2x80x9d to a rotatable shaft if it is directly fixedly mounted thereon, formed integrally therewith, or connected by any form of gearing or transmission that will transmit rotational power between the shaft and the compressor, turbine or fan. Thus, the rotation speed of the shaft may be different from the rotation speed of the device connected thereto.
The ventilation air duct (or auxiliary air line) connected to the auxiliary compressor can be connected to and direct the auxiliary ventilation air to an installation environment or installation space in which a respective air conditioning unit is installed, or to another compartment or space within the aircraft that requires positive forced ventilation at all times in a redundant and reliable manner. With this arrangement, the invention assures that whenever the first shaft of the air conditioning system is rotating, i.e. whenever this air conditioning unit is operating, the auxiliary compressor is also operating and providing cooling air to the installation space of the air conditioning unit, and/or to other spaces in the aircraft that require a constant ensured positive ventilation. Thus, whenever the respective air conditioning unit is operable, it can be ensured that its respective installation space is also properly ventilated and cooled, to avoid an overheating of the installation space and thereby avoid the necessity of shutting down an air conditioning unit (even though the air conditioning unit would otherwise be operational) merely because its installation space is becoming overheated.
It is further provided by detailed features of the invention, that the air conditioning system may include a second rotatable shaft with a second compressor and a second turbine connected thereto for rotation with this second shaft. The first compressor, second compressor, first turbine and second turbine may be connected in air flow series circuit to provide a two stage compression and expansion process with intercooling provided by one or more heat exchangers.
Also, the inventive air conditioning system may include a plurality of such air conditioning units that each includes a respective first shaft with a first compressor, a first turbine, and an auxiliary compressor mounted thereon. The ventilation air duct connected to the respective auxiliary compressor of each one of these air conditioning units can be connected in common to a ventilation air distribution duct, to ensure that the ventilation air can be provided redundantly to the various spaces that require constant positive ventilation, even in the event of the failure or malfunctioning of one of the several air conditioning units. The redundant or auxiliary air can alternatively or additionally be provided to one or more of the other air conditioning units to supplement or replace the compressed air needs of the air conditioning units in the event of the partial or total failure of one of the compressors thereof.